This invention relates generally to lightwave communication networks and, more particularly, to increasing the capacity of Wavelength Division Multiplexed (WDM) networks.
Wavelength Division Multiplexing (WDM) increases the capacity of lightwave communication systems by multiplexing many optical channels of different wavelengths for transmission as a composite signal in an optical fiber. At present, most WDM systems deployed in communication networks are generally considered to be low capacity systems, e.g., 4, 8, and 16-channel systems. With recent advances in optical networking technology, WDM system manufacturers are now contemplating systems having as many as 80 channels, for example. Although these higher capacity systems will help service providers in meeting the increasing demand for more bandwidth, service providers are also demanding cost-effective solutions for increasing the capacity of existing WDM systems while preserving the investments already made in these existing WDM systems.
Optical amplifiers, such as erbium doped fiber optical amplifiers, are important components in a WDM system. Unfortunately, most optical amplifiers used in existing WDM systems are limited in terms of usable gain bandwidth and, as a result, have limited utility for the emerging high capacity systems. Consequently, to increase the capacity of an existing WDM system, i.e., by adding more channels, a service provider generally must choose between the complete replacement of the existing lower capacity system with a higher capacity system or the installation of a second WDM system to operate in parallel with the existing WDM system.
In some cases, service providers are reluctant to completely replace existing systems with higher capacity systems because discarding existing equipment sacrifices a significant part of their initial investment. Moreover, a complete replacement would result in some system downtime during the replacement. Although a second WDM system installed to operate in parallel with the existing WDM system increases the overall system capacity from terminal to terminal, this option requires additional optical fiber which may not be available or may be too costly to install.
The costs and operational downtime associated with upgrading the capacity of existing WDM systems can be substantially reduced according to the principles of the invention with an optical filter/combiner arrangement that routes optical channels in two or more wavelength bands supplied by two or more WDM systems in the same optical fiber. The optical filter/combiner arrangement separates selected ones of the optical channels from each WDM system and supplies the separated optical channels to respective optical components in each of the WDM systems. After processing by the respective optical components, the optical channels are re-combined for simultaneous transmission in the same optical fiber. By simultaneously accommodating optical channels supplied by each of the WDM systems in the same optical fiber, a service provider can upgrade a first system to include optical channels from at least a second system without installing additional optical fiber and without discarding the existing WDM system.
In one illustrative embodiment, the optical filter/combiner arrangement includes a filter portion that receives a composite signal comprising optical channels in a first wavelength band supplied by a first WDM system and optical channels in a second wavelength band supplied by a second WDM system. The filter portion separates the optical channels into the two respective wavelength bands so that the optical channels in each of the wavelength bands can be supplied to a corresponding optical amplifier in each of the respective WDM systems. More specifically, the optical channels in the first wavelength band are routed to the optical amplifier in the first WDM system while the optical channels in the second wavelength band are routed to the optical amplifier in the second WDM system. After processing by the respective optical amplifiers, the optical channels in the two separate wavelength bands are re-combined in a combiner portion of the optical filter/combiner arrangement for simultaneous transmission as a composite signal in the same optical fiber.
In general, the optical filter/combiner arrangement according to the principles of the invention has practical utility for a variety of WDM network scenarios involving the combination of WDM systems operating in different wavelength bands in the same optical fiber. For example, the optical filter/combiner arrangement takes advantage of unused spectrum in an optical fiber for increasing capacity either through upgrades to existing WDM systems or with new DWDM system installations.